1. Field of the Invention
The present invention relates to a survivor capacity measuring apparatus for a battery preferably applied to an electric automotive vehicle.
2. Description of the Related Art
Various proposals have so far been made concerning a survivor capacity measuring apparatus for a battery for accurately indicating the survivor capacity of the battery.
Further, recently a demand has been made to provide means for determining on the deterioration of the battery and indicating it to a user as well as for accurately indicating the survivor capacity of the battery.
In general, for making judgment on the deterioration of the battery, it is considered that there are the following two methods.
First, there can be pointed out the method according to which the deterioration of the battery is determined by the use of the relationship between the internal resistance and the amount of discharge of the battery, that is, the relationship that the amount of discharge increases in proportion to the increase in the internal resistance.
However, in the case of such a method, the result of the measurement varies depending on the temperature, how the charging and discharging proceed, etc., so that it is difficult to determine the deterioration of the battery in some cases.
Next pointed out is the method according to which the amount of discharge current with respect to the amount of charging current is measured, so that, by the use of the result of this measurement, the deterioration of the battery is determined, more concretely, the value obtained by dividing the amount of discharge current by the amount of charging current is taken up as the degree of deterioration of the battery.
However, according to such a method, an integration error is produced as in the case of measuring the survivor capacity of the battery by the use of the current integrating system.
In particular, in the case that a regenerative current is produced in an electric automobile or the like, when the travailing speed of said electric automobile or the like is reduced or when it is travailing along a downward slope, there is the tendency that the errors due to the regenerative current accumulate, and as a result, an accurate measurement can hardly be made.
In connection with the case where such a regenerative current is generated, it is considered to use a structure constructed in such a manner that the survivor capacity is measured by the use of the current integrating system only when the automobile is in a high load state (as in the case of travailing along an ascending slope or the like) during which no regenerative current is produced, but anyway such a method that is based on dividing the amount of discharge current by the amount of charging current cannot be said to be a timely and accurate measurement method.